Superconductor LEDs Help Unravel Entanglement

Entanglement occurs when particles become correlated in pairs to predictably interact with each other, regardless of how far apart they are.

Researchers from the University of Toronto are developing a new method for generating entangled photons by combining LEDs with a superconductor. They say that this could introduce a rich spectrum of new physics as well as devices for quantum technologies, such as quantum computers and quantum communication.

"A usual light source such as an LED emits photons randomly without any correlations," said Alex Hayat, team leader at the Canadian Institute for Advanced Research. "We've proved that generating entanglement between photons emitted from an LED can be achieved by adding another peculiar physical effect of superconductivity — a resistance-free electrical current in certain materials at low temperatures.”

This effect occurs when electrons are entangled in Cooper pairs: two electrons spinning in opposite directions.

When the researchers placed a layer of superconducting material in close contact with a semiconductor LED structure, Cooper pairs were injected into the LED, resulting in pairs of entangled electrons creating entangled pairs of photons.

However, this works only with LEDs that use nanometer-thick active regions, or quantum wells.

"Typically quantum properties show up on very small scales — an electron or an atom,” Hayat said. “Superconductivity allows quantum effects to show up on large scales — an electrical component or a whole circuit.”

He noted that this quantum behavior could significantly enhance light emission in general, and entangled photon emission in particular.

A charged elementary particle of an atom; the term is most commonly used in reference to the negatively charged particle called a negatron. Its mass at rest is me = 9.109558 x 10-31 kg, its charge is 1.6021917 x 10-19 C, and its spin quantum number is 1/2. Its positive counterpart is called a positron, and possesses the same characteristics, except for the reversal of the charge.

A metal, alloy or compound that loses its electrical resistance at temperatures below a certain transition temperature referred to as Tc. High-temperature superconductors occur near 130 K, while low-temperature superconductors have Tc in the range of 4 to 18 K.